This invention relates to a pattern display system wherein a color pattern is displayed by scanning a picture screen through raster scanning.
To display various chromatic patterns such as characters, figures or symbols at arbitrary positions on a picture screen by a control system having a program processing function such as by a micro-processor, it has been general practice to store programmable pattern positions, pattern shapes and color data in memories and to display a color pattern sequentially on picture elements by addressing the memories. In such a conventional practice, in order to provide color data for each pattern, the color information is read out directly from a memory which stores color information at positions corresponding to the pattern through DMA (Direct Memory Access) and sent to a color difference generator circuit which produces predetermined color signals which control the irradiation of beams of electron for color display. Generally, at least three memories are required for storing each color information of red, blue and green, each memory having a memory capacity equal to the number of patterns to be displacyed on the picture screen. Therefore, with three memories for storing color information of respective red, blue and green, the number of colors corresponding to the color data storage in each memory, i.e., 2.sup.3 =8 can be displayed. More particularly, there can be displayed three colors of red, blue and green and five additional colors accuring from possible combinations of the three colors, namely, red+blue=magenta, red+green=yellow, blue+green=cyan, red+blue+green=white, and black. However, with recent trend to display complicated patterns, the types of colors have been diversified in order to clearly display each pattern. To meet such a trend, it is necessary to change mixing percentage of red, blue and green by increasing the number of color data storing memories. However, increased memories will inconveniently raise the cost. Further, when it is desired that the number of patterns to be displayed on the picture screen be increased and high resolution be required of the pattern, the capacity required for one memory increases, adding more economic burdens.